(1) Field of the Invention
The present invention relates to a process for the preparation of silicon-containing isocyanate compounds. More particularly, it relates to a process for the preparation of a silylalkyl isocyanate compound having an alkoxy-silicon linkage, which is valuable as the starting material for the production of various silyl group-containing compounds.
(2) Description of the Related Art
As an example of the process for the production of a silicon compound as described above, a process is known in which a corresponding alkoxysilane and allyl isocyanate are subjected to addition reaction at a high temperature in the presence of rhodium trichloride to prepare an alkoxysilylpropyl isocyanate (see Japanese Examined Patent Publication No. 55-40,592). This process, however, has problems in that the catalyst used is expensive, the reaction must be carried out at a high temperature, and the product is limited to a silylpropyl isocyanate.
As other examples, there are known a process in which a corresponding silylalkylamine is converted to a halosilyl ester of carbamic acid and the ester then decomposed (see U.S. Pat. No. 4,064,151) and a process in which a corresponding silylalkylamine is converted to a methyl ester of carbamic acid and the ester then thermally decomposed in vacuum (see U.S. Pat. No. 3,494,951). In these processes, however, since the starting material is first converted to a carbamate and the carbamate then decomposed, the number of steps in the process is increased. Moreover, the manufacturing cost is increased by using the starting material in the form of a carbamate ester, or by the recovery thereof. Especially, in the latter process, since heating is conducted at a high temperature in vacuum, the reaction apparatus becomes complicated and the equipment cost is increased.
Therefore, the industrial production of an isocyanate compound has been generally carried out through a reaction between an amine and carbonyl chloride.
However, in the conventional reaction between a silylalkyl amine having an alkoxy-silicon linkage and carbonyl chloride, the alkoxy group is preferentially chlorinated and the intended product cannot be obtained (see Example 1 of Japanese Examined Patent Publication No. 42-23,171).
Furthermore, in the reaction between an aminoalkyldisiloxane (free of an alkoxy group) and carbonyl chloride, only a two-stage process is known in which a trimethylsilyl group is first introduced into the amino group (see French Pat. No. 1,563,380).